Australian Fur Seal (Arctocephalus pusillus doriferus), originally found widely along the shores in southeastern Australia, now breeds only on a few offshore islands near southeast Australia. However, populations are now increasing and may now be considered locally common. The Fur Seals (genus Arctocephalus) were historically hunted for their valuable fur.

Eared Seals (Family Otaridae) contains the Walrus, California Sea Lion, and the Fur Seal. Sometimes the Walrus is placed alone in a separate family called Odobaenidae or even placed in the Phocidae. The fifteen species in this group are organized into eight different genera. Following is a list of most of the species in this family:

Walruses and Seals (Order Pinnipedia) are a group of marine animals that are especially abundant in cold areas particularly near the poles. These animals are characterized by front and rear legs that have modified into flippers for swimming. They spend most of their lives in water, and are not especially adapted for living on land. Most species feed on fish, marine Crustacea, and other vertebrates. Because these animals are closely related to the carnivores, they could be combined with the carnivore group into one large order.

Mammals (Class Mammalia), together with the birds, are among the youngest of the classes of animals. In species count, mammals number about fifty-one hundred, trailing reptiles (approximately fifty-five hundred), fish (approximately eighteen thousand), and birds (approximately eighty-six hundred).

marsupials
Newborn emerges very underdeveloped and continue to
mature in a pouch on its mother's abdomen (i.e., opossums,
koala, kangaroo)

placental
Embryo develops within the uterus of the female and is
dependent on a placenta for nutrition and waste removal
(i.e., humans, lions, monkeys)

About sixty-five million years ago, the Tertiary era produced thirty-five orders of mammals. Of this number, eighteen have survived to represent Earth's most diversified as well as its most highly developed classification of animals.

Extinction of mammals is fast becoming a serious issue. Duff and Lawson present a list of forty-one extinct species that reached extinction prior to 1800. These forty-one species are not acknowledged in the counts of the various families. Duff and Lawson also present a list of forty-six species including three gazelles, one zebra, one seal, one deer, and one wolf that have probably gone extinct since 1800. These forty-six species are included in the family counts. Science is adding about forty to fifty new species a year to the list. Many of these are the result of divisions of prior species; some are recent discoveries.

Mammals owe their survival to adaptive capabilities that include the ability to exploit whatever sources of food are available to them, as well as their ability to adjust to various climes. Food specialization influenced evolution to such a great extent that the teeth structure can and has been used to provide extensive information on the food needs and various lifestyles of extinct species.

Despite the vast diversity among mammals in terms of size, habitats and adaptations, they share without exception many characteristics such as:

Backboned Animals (Phylum Chordata) are the most advanced group of animals on earth. These animals are characterized by having a spinal cord or backbone. Most members have a clearly defined brain that controls the organism through a spinal cord. Fish, amphibians, reptiles, birds, and mammals are in this phylum.

Currently, some taxonomists believe that the fish should be divided into two groups (sharks and regular fishes) and that there are some other primitive groups in the phylum such as hagfish or lampreys.

Animal Kingdom contains numerous organisms that feed on other animals or plants. Included in the animal kingdom are the lower marine invertebrates such as sponges and corals, the jointed legged animals such as insects and spiders, and the backboned animals such as fish, amphibians, reptiles, birds, and mammals.